[rules-users] New in Drools, java.lang.NullPointerException at org.drools.reteoo.AccumulateNode.getFirstMatch(AccumulateNode.java:967)

Hello all! I am new in Drools but day by day, test by test, I think I get a bit more knowledge of how the rule engine works from user point of view. I've been adding rules to an alarm system, increasing the complexity and functionality in several steps. Unfortunately in the last step I found the following NullPointerException inside the rule engine... java.lang.NullPointerException at org.drools.reteoo.AccumulateNode.getFirstMatch(AccumulateNode.java:967) at org.drools.reteoo.AccumulateNode.modifyLeftTuple(AccumulateNode.java:329) at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateModifyChildLeftTuple(SingleLeftTupleSinkAdapter.java:239) at org.drools.reteoo.AccumulateNode.evaluateResultConstraints(AccumulateNode.java:640) at org.drools.reteoo.AccumulateNode.assertObject(AccumulateNode.java:270) at org.drools.reteoo.BetaNode.modifyObject(BetaNode.java:312) at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateModifyObject(CompositeObjectSinkAdapter.java:460) at org.drools.reteoo.CompositeObjectSinkAdapter.propagateModifyObject(CompositeObjectSinkAdapter.java:428) at org.drools.reteoo.AlphaNode.modifyObject(AlphaNode.java:160) at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateModifyObject(CompositeObjectSinkAdapter.java:460) at org.drools.reteoo.CompositeObjectSinkAdapter.propagateModifyObject(CompositeObjectSinkAdapter.java:428) at org.drools.reteoo.ObjectTypeNode.modifyObject(ObjectTypeNode.java:263) at org.drools.reteoo.EntryPointNode.modifyObject(EntryPointNode.java:172) at org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1442) at org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1349) at org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:183) at org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:196) at es.simcasva.alarmas.rules.Rule_Test_Negativo_Alarma_Acceso_Portal_Ubicacion_UM_0.defaultConsequence(Rule_Test_Negativo_Alarma_Acceso_Portal_Ubicacion_UM_0.java:18) at es.simcasva.alarmas.rules.Rule_Test_Negativo_Alarma_Acceso_Portal_Ubicacion_UM_0DefaultConsequenceInvoker.evaluate(Rule_Test_Negativo_Alarma_Acceso_Portal_Ubicacion_UM_0DefaultConsequenceInvoker.java:44) at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:917) at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:856) at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1071) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:785) at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:751) at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:218) I've been trying to find the problem, and found a strange interaction between three rules that makes the null pointer to appear. The alarm system has many rules now and it is difficult to simplify the scenario, so I just would like to know what is the funcion of AccumulateNode object in order to have an idea of the NullPointerException possible cause. Can anyone help me? Thank you in advance for your time. Regards, Manuel Ortiz.